Electronic device with noise-cancelling force sensor

• US 9,983,716 B2
• Filed: 10/02/2017
• Issued: 05/29/2018
• Est. Priority Date: 12/16/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Yang, Bingrui, Grunthaner, Martin P., Hotelling, Steven P.
• Primary Examiner(s): Bolotin, Dmitriy
• Application Number:
  US15/722,999
• Publication Number:
  US 20180024687A1
• Time in Patent Office: 239 Days
• CPC Class Codes: G01L 1/22 using resistance strain gauges
• CPC Class Codes: G01L 1/2262 involving simple electrical bridges
• CPC Class Codes: G06F 2203/04102 Flexible digitiser, i.e. constructional details for allowing the whole digitising part of a device to be flexed or rolled like a sheet of paper
• CPC Class Codes: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position
• CPC Class Codes: G06F 3/0414 using force sensing means to determine a position
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: G06F 3/047 using sets of wires, e.g. crossed wires
• CPC Class Codes: H03K 17/9625 using a force resistance transducer
• CPC Class Codes: H04M 1/0266 for a display module assembly
• CPC Class Codes: H04M 1/72466 with selection means, e.g. keys, having functions defined by the mode or the status of the device
• CPC Class Codes: H04M 1/72469 for operating the device by selecting functions from two or more displayed items, e.g. menus or icons

Abstract

An electronic device may have a housing in which components such as a display are mounted. A strain gauge may be mounted on a layer of the display such as a cover layer or may be mounted on a portion of the housing or other support structure. The layer of material on which the strain gauge is mounted may be configured to flex in response to pressure applied by a finger of a user. The strain gauge may serve as a button for the electronic device or may form part of other input circuitry. A differential amplifier and analog-to-digital converter circuit may be used to gather and process strain gauge signals. The strain gauge may be formed form variable resistor structures that make up part of a bridge circuit that is coupled to the differential amplifier. The bridge circuit may be configured to reduce the impact of capacitively coupled noise.

Claims

1. A strain gauge, comprising:

a layer of material configured to flex in response to pressure;

a first variable resistor mounted on the layer of the material;

a second variable resistor mounted on the layer of the material adjacent to the first variable resistor; and

a differential amplifier having first and second differential inputs that receive input from a bridge circuit and having an output at which a corresponding strain gauge output signal is provided, wherein the bridge circuit includes the first and second variable resistors, wherein the first variable resistor follows a path on the layer of material, wherein the second variable resistor follows the same path on the layer of material, and wherein the path is a serpentine path.

2. The strain gauge defined in claim 1, wherein the bridge circuit further comprises first and second fixed resistors.

3. The strain gauge defined in claim 2, wherein the first and second variable resistors have equal areas.

4. The strain gauge defined in claim 1, wherein the first and second variable resistors have the same shape and the same area on the layer of material.

5. The strain gauge defined in claim 1, wherein the layer of material comprises a layer of material associated with a display.

6. The strain gauge defined in claim 5, wherein the layer of material associated with the display comprises a display cover layer.

7. The strain gauge defined in claim 1, wherein the serpentine path comprises a first plurality of substantially parallel portions that are connected by a second plurality of substantially parallel portions.

8. The strain gauge defined in claim 1, wherein the serpentine path has a first portion extending in a first direction, wherein the path has two turns connecting the first portion to a second portion, and wherein the second portion extends in a second direction that is the opposite of the first direction.

9. A strain gauge, comprising:

a layer of material configured to flex in response to pressure;

at least one variable resistor mounted on the layer of the material;

a differential amplifier having first and second differential inputs that receive input from a bridge circuit and having an output at which a corresponding strain gauge output signal is provided, wherein the bridge circuit includes the at least one variable resistor; and

a coupling pad that balances how much noise is capacitively coupled to the first differential input with how much noise is capacitively coupled to the second differential input.

10. The strain gauge defined in claim 9, wherein the at least one variable resistor comprises first and second variable resistors and wherein the coupling pad is coupled to the first variable resistor.

11. The strain gauge defined in claim 10, wherein the bridge circuit includes first and second fixed resistors.

12. The strain gauge defined in claim 11, wherein the first and second fixed resistors are formed using surface mount technology components.

13. The strain gauge defined in claim 9, wherein the at least one variable resistor comprises a first variable resistor and wherein the coupling pad is coupled to the first variable resistor.

14. The strain gauge defined in claim 13, wherein the bridge circuit includes first, second, and third fixed resistors.

15. The strain gauge defined in claim 14, wherein the first, second, and third fixed resistors are formed using surface mount technology components.

16. A strain gauge, comprising:

a layer of material configured to flex in response to pressure;

a first variable resistor mounted on the layer of the material;

a second variable resistor mounted on the layer of the material, wherein the second variable resistor overlaps the first variable resistor; and

a differential amplifier having first and second differential inputs that receive input from a bridge circuit and having an output at which a corresponding strain gauge output signal is provided, wherein the bridge circuit includes the first and second variable resistors.

17. The stain gauge defined in claim 16, wherein the first and second variable resistors have the same shape and size on the layer of material.

18. The strain gauge defined in claim 16, wherein the bridge circuit includes first and second fixed resistors and wherein the first and second fixed resistors are formed using surface mount technology components.